I. Field of the Invention
The present invention relates to communications. More particularly, the present invention relates to a system and method for performing service negotiation as initiated by a subscriber unit or a base station.
II. Description of the Related Art
The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of system users are present. Although other techniques such as time division multiple access (TDMA), frequency division multiple access (FDMA), and amplitude modulation (AM) schemes such as amplitude companded single sideband (ACSSB) are known, CDMA has significant advantages over these other techniques. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS," assigned to the assignee of the present invention and incorporated by reference herein.
In the wireless CDMA system, a large number of wireless subscriber units, each having a transceiver, communicates through satellite repeaters or terrestrial stations which are also referred to as cells. Each cell includes a physical plant called a base station. A cell covers a limited geographic area and routes calls carried over subscriber units to and from a telecommunication network via a mobile switching center. When a subscriber moves into the geographic area of a new cell, the routing of that subscriber's call may be eventually made through the new cell by a process called a "handoff."
A subscriber unit transmits a signal that is received by a base station. The signal is then relayed to a mobile switching center which in turn routes the signal to the public switched telephone network and to telephone lines or other subscriber units. Similarly, a signal may be transmitted from the public switched telephone network to a subscriber unit via a base station and a mobile switching center. The communications channel allocated for communication of information between the subscriber unit and the base station is called the traffic channel.
The interface between the subscriber unit and the base station is referred to as the air interface. The telecommunications industry association (TIA) has provided a standard for CDMA call processing on the air interface entitled "IS-95 Mobile Station - Base Station Compatibility Standard for Dual Mode Wideband Spread Spectrum Cellular System." Addendum to IS-95 are provided as Telecommunications Service Bulletins (TSB). The standard IS-95+TSB74 includes provisions for service negotiation on the air interface and is incorporated herein by reference. The interface between the base station and the mobile switching center is referred to as the A interface. The TIA has provided for call processing on the A interface through the standard provided in "IS-634 Mobile Switching Center - Base Station Interface for Public 800 MHz," which is also incorporated herein by reference. IS-95-A and IS-634 both define the messages and signals that are sent on their respective interfaces for the operation of a CDMA wireless system.
The call flow in a CDMA system requires processing on both the air interface and the A interface. The successful progression of a call requires that the proper messages and signals are sent at the right times on both the air interface and the A interface. The IS-634 standard is being developed to provide for call processing on the A interface. A number of problems and deficiencies are present in IS-634 which currently does not support some of the necessary operations on the A interface.
One deficiency in IS-634 is in the handling of the service negotiation procedure. Service negotiation is performed between a subscriber unit and a base station to determine the air interface configuration for different services. The configuration includes the forward and reverse transmission rates, the forward and reverse framing formats (multiplex option), and the services associated with different logical connections (service options). Service options refer to the service capabilities of the system, and may be applications such as voice, data, facsimile, or SMS.
Although messages associated with service negotiation are well defined for the air interface, messages must also be defined for the A interface to support the service negotiation procedure. The mobile switching center needs to be involved in service negotiation because it stores information necessary for service negotiation and authorizes use of any specific service configuration for a call. The information may not otherwise be available to the base station and the subscriber unit. The information stored in the mobile switching center includes the Subscribed Services Record, which lists the services that a subscriber unit is authorized to use. The Subscribed Services Record needs to be accessed to properly negotiate the service configuration for the subscriber unit.
Additionally, A interface messages may be needed to properly handle a service negotiation procedure which is occurring while the call is in a soft handoff across multiple base stations. A handoff may be necessary if a subscriber unit moves from the coverage area of a source base station to the coverage area of target base station or base stations. In a soft handoff using circuit mode transport for inter base station communication, the source and target base stations do not communicate directly with one another. Instead, they communicate via the mobile switching center. Thus, if service negotiation occurs while the call is in soft handoff, the parameters associated with the negotiated service configuration must be provided to the target base stations through the mobile switching center. The A interface protocol should accommodate this function.
These problems and deficiencies are recognized and solved by the present invention in the manner described below.